The present invention relates generally to a PCM signal recording method and a PCM signal recording/reproducing apparatus and more particularly to a data recording method and a data processing circuit suited profitably for recording and/or reproduction of PCM audio signals.
Heretofore, a digital audio tape recorder system (referred to as DAT system in abbreviation) is known as an apparatus for recording/reproducing audio PCM signals. Concerning the recording format adopted in such DAT systems, discussion is found in "THE DAT CONFERENCE, DIGITAL AUDIO TAPE RECORDER SYSTEM", June, 1987, pp. 45-54.
With the structure of the recording format for the DAT system disclosed in the above literature, data of two channels each having a sampling frequency of 48 KHz and a quantization bit number of 16 bits are compatible with the data of two channels each having a sampling frequency of 32 KHz and a quantization bit number of 16 bits, and these data of respective formats can be recorded and reproduced without any need for a complicated switching (exchange) circuit.
Further known is an audio system for performing recording/reproduction of PCM audio signals of two channels having a sampling frequency of 48 KHz and a quantization bit number of 16 bits, which apparatus additionally includes a data conversion circuit having a data format converting or translating function so that four channel audio PCM signals each having a sampling frequency of 32 KHz and a quantization bit number of 12 bits can be recorded and reproduced, as is disclosed in JP-A-61-236074.
However, in the prior art DAT systems mentioned above, no consideration is paid to the compatibility between the four channel mode in which the sampling frequency (f.sub.s) is 32 KHz and the quantization bit number is 16 bits and the two channel mode where the sampling frequency (f.sub.s) is 32 KHz and the quantization bit number is 16 bits. Accordingly, the recording/reproduction apparatus designed for the audio PCM signals of two channels having the sampling frequency of 48 KHz and the quantization bit number of 16 bits on one hand and the PCM signals of the two channels having the sampling frequency of 32 KHz and the quantization bit number of 16 bits on the other hand is incapable of reproducing the recorded audio PCM signals of the four channels each having a sampling frequency of 32 KHz and a quantization bit number of 16 bits. Further, for making it possible to reproduce the four channel data mentioned above, such a circuit which is capable of recording/reproducing the data of two channels at the sampling frequencies of 48 KHz and 32 KHz, respectively, with the quantization bit number of 16 bits must be additionally provided in association with a complicated data switching circuit.
In the system capable of performing the recording and the reproduction with the format for the four channels each having the sampling frequency of 32 KHz and the quantization bit number of 12 bits, as disclosed in JP-A-236074, the recording/reproduction of data of two channels having the sampling frequency of 32 KHz and the quantization bit number of 16 bits can be rendered only by performing 16-to-12 bit compression and 12-to-16bit expansion on the audio PCM signal and by using the format for only two of the four channels. In that case, compatibility may be ensured between the audio PCM signals of four channels having the sampling frequency of 32 KHz and the quantization bit number of 12 bits and the audio PCM signals of two channels having the sampling frequency of 32 KHz and the quantization bit number of 16 bits.
However, such system is disadvantageous in that the circuits for 16-to-12 bit compression and 12-to-16 bit expansion are additionally required and suffers a problem that the audio PCM signals of two channels having the sampling frequency of 32 KHz and the quantization bit number of 16 bits is subject to deterioration in the performance or quality due to the compression and expansion mentioned above.